Within an hour of exposure to erythropoietin, erythroid progenitor cells show a marked up regulation of the protein TAXREB107, yet almost nothing is known of the role this protein plays in the subsequent differentiation of these cells. Two branches of investigation are proposed here. The first is aid at illuminating the control of the taxreb107 gene and will address what cell components are required for its upregulation. The dependence of upregulation on protein synthesis, and on the enzymes PKC, Pptase, and JAK2 (which are known to be involved in other branches of the Epo signal pathway) will be determined. It will also be resolved whether upregulation is controlled at the level of transcription or by the stabilization of mRNA. The second branch of investigation is concerned with the role TAXREB107 plays in the cell. The effects of the protein on differentiation will be examined and the DNA site wo which it binds will be identified. Finally, an attempt will be made to find cellular proteins with which TAXREB107 interacts directly. The results of these experiments should greatly improve our understanding of what promises to be an important molecule in the process of erythropoiesis.